1. Field of the Invention
This invention relates generally to an iterative decoder. More particularly, the present invention relates to an iterative decoder for application in either digital data transmission or digital data storage and a method embodied therein.
2. Background Information
FIG. 1 illustrates a conventional digital data transmission system. As shown therein a digital data transmission system comprises a transmitting section 300 for transmitting data to receiver 500 via communication channel 401. During the transmission operation shown in FIG. 2, the data is first encoded in a conventional manner by run length limited (RLL) encoder 302 or RLL encoder means, and parity bits are encoded by linear block code encoder 304 or linear block encoder means. The combined RLL encoded data and parity bits are then input to transmitter 306 or transmitting means for transmission as an analog, electrical signal over communication channel 401. Communication channel 401 may include any wireless, wire, optical and the like communication medium. Receiver 500 comprises an analog to digital converter 502 or analog to digital converting means to converts the data transmitted on communication channel 401 to a digital signal. The digital signal is input to soft channel decoder 504, which provides probability information of the detected data. Soft linear block code decoder 506 utilizes this information and the parity bits. Soft channel decoder 504 and soft linear block code decoder 506 operate in an iterative manner to decode the detected data.
Linear block codes are well known to those of ordinary skill in the art. One example of a linear block code is a low density parity check code (LDPC) which is discussed by Robert G. Gallager in Low-Density Parity-Check Codes, 1963, M.I.T. Press and by Zining Wu in Coding and Iterative Detection For Magnetic Recording Channels, 2000, Kluwer Academic Publishers, the contents of each of which are incorporated in their entirety by reference.
FIGS. 2a-2c show a digital data storage system. As illustrated in FIG. 2a, hard disk drive 100 comprises a magnetic disk and head assembly 104 including a stack of several rigid magnetic disks 102 and several magnetic transducers positioned on a movable arm 105 for operable interaction with the magnetic recording surfaces on each disk. These magnetic heads slide or ‘fly’ in close proximity over the surfaces of the magnetic disks 102 to react to the changes in orientations of magnetic fields of tiny magnetic domains on the disks that represent the stored data. These interactions with magnetic fields produce electrical signals of constantly varying amplitudes that are pre-amplified to produce resulting analog waveforms 106, as shown in FIG. 2b, that are applied to a read-channel integrated circuit 109, as shown in FIG. 2c. The read channel integrated circuit 108 processes the waveform and produces data-representing signals having digital waveforms 110, as shown in FIG. 2d. The same integrated circuit 108 is also used during data-writing processes to transform user data in digital form to analog waveforms that are then recorded on a disk 102 via the associated magnetic transducer.
FIG. 3 illustrates typical flow of data signals during write operations by encoder 600 onto disk drive 400 and read operations by read channel 700 from disk drive 400. During the write operation shown in FIG. 3, the data is first encoded, similarly to the digital data transmission system described above, by run length limited (RLL) encoder 302, and parity bits are encoded by linear block code encoder 304. The combined RLL encoded data and parity bits are then input to current generator 402 or writing means for generating a current to drive write head 404. Write head 404 magnetizes disk 406 for storing the data signal thereon.
In the reading process, read head 408 detects and converts the data stored on disk 406 to an analog, electrical signal. The electrical signal is converted to a digital signal in read channel 700 by analog to digital converter 502. The digital signal is input to soft channel decoder 504. Soft linear block code decoder 506 utilizes this information and the parity bits. Soft channel decoder 504 and soft linear block code decoder 506 operate in an iterative manner to decode the detected data.
One disadvantage of the conventional iterative decoding approach is that, even though this approach produces robust gains in terms of bit error rate (BER), it is susceptible to large error bursts caused by an inability of the iterative algorithm to converge within the allowed number of iterations. To exacerbate this situation, erroneous bits at the output to iterative detector do not necessarily cluster together. As such, it is more difficult for the error correcting code (ECC) to properly perform its function. Additionally, when utilizing LDPC errors can propagate. In other words, wrong information may be passed along the decoding process.